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ISSN 1006-9895

CN 11-1768/O4

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城市化对北京单次极端高温过程影响的数值模拟研究
作者:
作者单位:

1.中国气象局 国家气象信息中心;2.中国气象局气候研究开放实验室;3.中国地质大学环境学院大气科学系

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Numerical Simulation of Urban Effect on a Single Extreme High Temperature Event in Beijing
Author:
Affiliation:

1.Laboratory for Climate Studies,National Climate Center,China Meteorological Administration;2.Department of Atmospheric Science,School of Environmental Science,China University of Geosciences

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    摘要:

    城市化对高温热浪的频次和强度具有重要影响,但目前对于城市化影响高温热浪过程的机理了解还不充分。本文利用WRF模式,对2010年7月2-6日北京一次高温过程进行了模拟,分析了城市化对此次高温过程的影响机理。采用优化后的WRF模式,能够模拟出北京连续5日高温的特征和城市热岛强度的变化。城市下垫面的不透水性决定了城区2m相对湿度低于乡村,削弱了城区通过潜热调节城市气温的能力。日落后,城市感热通量下降缓慢,城区降温速率小于乡村,夜间边界层稳定、高度低,风速小,抑制了城乡之间能量的传输,形成了夜间强的城市热岛强度,相对乡村显著增幅了夜间高温。日出后城乡地面感热通量、潜热通量迅速上升,边界层稳定性下降。午后,城市下垫面分别为地表感热通量和潜热通量的高、低值中心,通过潜热调节气温的能力被削弱;边界层稳定度弱,有利于能量的垂直扩散;此时,城市热岛强度小于夜间。7月5日出现极端高温,除了较强的城市热岛效应外,中国东部大部分地区受到大陆暖高压控制,北京处于高压脊前,西北气流越山后的焚风效应进一步加剧了北京当日高温强度。因此,在此次极端高温过程中,北京城市下垫面形成了明显的城市热岛效应,加重了城区极端高温事件的强度。

    Abstract:

    Urbanization has an important influence on the frequency and intensity of heat waves, but the mechanism of urbanization affecting the process of high temperature is not fully understood. The Weather Research and Forecasting (WRF) model is used to simulate a summer high-temperature process in Beijing from 2 to 6 July 2010. This paper reports the main results of urbanization effect on surface air temperature of urban areas in the heat wave process. It is found that the optimized WRF model is able to simulate the temporal characteristics of the 5 consecutive days of high temperature and the variation of IUHI (urban heat island intensity) in Beijing. The impermeability of urban underlying surface determines that the 2m relative humidity of urban area is lower than that of rural area, which weakens the ability of urban area to regulate surface air temperature through latent heat. After sunset, the urban sensible heat flux decreases slowly, and cooling rate of urban area is less than that of rural area. At night, the structure of boundary layer is stable and the height of it is low, and the wind speed is small. In this case, the energy transmission between urban and rural areas is restrained, forming a strong urban heat island at night. After sunrise, sensible heat flux and latent heat flux of urban and rural land surface rise rapidly, and the stability of boundary layer decreases. In the afternoon, the urban underlying surface is in favor of the high and low value centers of sensible heat flux and latent heat flux respectively, with the ability to regulate temperature through latent heat weakened. It’s conducive to the energy vertical transfer that the stability of the boundary layer is weak. The IUHI in the afternoon is smaller than that in evening. The extreme high temperature occurred on 5 July. An abnormal continental warm high pressure controls most parts of China, and Beijing is in front of the high-pressure ridge. The Fohn effect of the northwesterly flowing over the mountains aggravated the urban high temperature except for the larger IUHI. In this process of heat wave, therefore, the obvious urban heat island effect created by the urban underlying surface in Beijing has increased the strength and severity of the extreme high temperature event.

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  • 收稿日期:2019-10-15
  • 最后修改日期:2020-01-02
  • 录用日期:2020-04-27
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